I recently retired my old Dell Mini 9 from streamer\front end duty. It works just fine but all the newer software were really challenging the poor thing and it was beginning to cut out during playback. Keep in mind that this thing was running with an ancient Atom N270 processor, and I sped it up a good deal with a new Ncore SSD a few years back. I got a new XPS so my old one got downgraded to the audio rack, and the Mini 9 went in a drawer. Given its fanless nature, I thought about using a Linux distro with it to lighten up the CPU load, but remembered the driver issues I had the first time I tried that and thought better of it. Depending on your netbook, that might also be a valid path for you.
All that goes to say that as long as you're not getting audible noise or variations in sound during playback, most USB outputs from laptops, including netbooks, are just fine, IMO.
Now, I will leave it to the experts to chime in on if there is a simple way to test the levels of jitter (or dropped packets) the USB port is outputting, but honestly, a good DAC should be able to sort that out and give you a good analog output.